Stability, electronic structure, mechanical properties and lattice thermal conductivity of FeS and FeS2 polymorphs

First-principles calculations were used to investigate the stability, electronic structure, elastic and lattice thermal conductivity of FeS and FeS2 polymorphs ([Formula: see text]-FeS, [Formula: see text]-FeS, [Formula: see text]-FeS, [Formula: see text]-FeS2, [Formula: see text]-FeS2). The calculated lattice parameters were in agreement with experimental results. The results showed that these Fe-S binary compounds are thermodynamically and mechanically stable. The elastic anisotropies of Fe-S binary compounds were exhibited by 3D modulus ball and 2D projections. Among all the five compounds, [Formula: see text]-FeS2 compound has the largest bulk modulus and [Formula: see text]-FeS2 has the largest Young’s modulus and hardness. Furthermore, [Formula: see text]-FeS, [Formula: see text]-FeS and [Formula: see text]-FeS compounds can be regarded as ductile material according to [Formula: see text] and Poisson’s ratio. The FeS compounds show metallic character and FeS2 compounds show semiconductor character through analyzing their bandgap and density of states (DOS). The [Formula: see text]-FeS2 has the largest thermal conductivity according to the Clarke model, and the [Formula: see text]-FeS shows the strongest thermal conductivity anisotropy among the five compounds.

Структура и электропроводность перовскитов Pr-=SUB=-1-x-=/SUB=-Sr-=SUB=-x-=/SUB=-MnO-=SUB=-3-=/SUB=- (x=0; 0.15; 0.25)

Pr1-xSrxMnO3 manganites (x=0; 0.15; 0.25) were synthesized by the solid-phase method at a temperature of 1250°C and have an orthorhombic perovskite-like structure (space group Pbnm). A comprehensive study of the effect of praseodymium substitution with strontium on the temperature features of the transformation of the crystal structure of the studied perovskites was performed using high-temperature radiography and differential thermal analysis. It was determined that the temperature of the Jahn-Тeller effect significantly decreases with the introduction of strontium. It is established that all samples have a semiconductor character of conductivity. Strontium doping significantly increases the electrical conductivity of praseodymium manganites, especially at temperatures below 450°C.

Фотоэмиссионные исследования электронной структуры GaN, выращенного методом молекулярно-пучковой эпитаксии с плазменной активацией азота

The results of experimental studies of the electronic and photoemission properties of an epitaxial GaN layer grown on a SiC/Si(111) substrate by plasma assisted molecular beam epitaxy are presented. The electronic structure of the GaN surface and ultrathin Li/GaN interface was first studied in situ under ultrahigh vacuum conditions under different Li coverages. The experiments were performed using photoelectron spectroscopy with synchrotron radiation in the photon energy range of 75–850 eV. The photoemission spectra in the region of the valence band and surface states and the photoemission spectra from the N 1s, Ga 3d, Li 2s core levels were studied for different submonolayer Li coverages. It is established that Li adsorption causes significant changes in the general form of the spectra induced by charge transfer between the Li layer and the lower N and Ga layers. It is established that the GaN surface has predominantly N-polarity. The semiconductor character of the Li / GaN interface is shown.

Horseradish Peroxidase Immobilized on Polyaniline onto Monocrystalline Silicon for Glyphosate Herbicide Detection

In this work a special electrode configuration with potential application in enzymatic biosensors for the detection of glyphosate was studied. The enzyme used was Horseradish Peroxidase (HRP), which was immobilized on a polyaniline film (PAni), electrodeposited on the surface of the n-type monocrystalline silicon electrode. PAni has the ability to bind to biomolecules and thereby potentiate their biocatalytic properties by favoring the transfer of electrons between enzyme and substrate. Monocrystalline silicon is one of the most used materials in electronic technology due to its semiconductor character. In this work, different parameters were investigated in the electrode preparation, including concentration of polyaniline in the electrodeposition solutions, as well as the electrodeposition times and potentials. The response of the electrode as biosensor was evaluated by the electric current density characteristic of hydroquinone oxidation in the presence of standardized glyphosate solutions. The peroxidase enzyme catalyzes the oxidation of hydroquinone to the o-quinone form in the presence of hydrogen peroxide. In turn, glyphosate inhibits the activity of HRP and causes a reduction of the electric current density in the biosensor electrode. The results obtained with glyphosate using the proposed method are in agreement with the literature and show that the n-Si/PAni/HRP biosensor maintains the catalytic activity and is of considerable interest due to the simple procedure in practical applications and a promising platform for the lack of environmental monitoring for these contaminants.

Modulation of band gap and p- versus n-semiconductor character of ADA dyes by core and acceptor group variation

By variation of donor and acceptor building blocks in acceptor–donor–acceptor dyes a transition from p- to n-type semiconductor has been achieved.

Transverse resistance in HoBa2Cu3O7−δ single crystals

The transverse electrical resistance of HoBa2Cu3O[Formula: see text] single crystals is investigated in the temperature range [Formula: see text] for optimally-doped [Formula: see text] and oxygen-poor [Formula: see text] samples. With decreasing temperature, the resistivity of the optimally-doped samples has been found to transit from the regime of scattering on phonons and defects to the regime of “semiconductor” character and, near [Formula: see text], of the fluctuation conductivity. The oxygen-poor samples have been revealed to exhibit only a variable range hopping conductivity of “semiconductor” character, which near [Formula: see text] transits into the fluctuation conductivity. A significant anisotropy of the residual resistivity and characteristics of the fluctuation conductivity is observed for samples of both types.

First-Principles Study on Structural and Electronic Properties of the Armchair GaN Nanoribbons

Calculations have been performed for the structures and electronic properties of GaN nanoribbons with armchair edge (AGaNNRs), using the first-principles projector-augmented wave (PAW) potential within density functional theory (DFT) framework. The lowest unoccupied conduction band (LUCB) and the highest occupied valence band (HOVB) are always separated, representing a semiconductor character for the AGaNNRs. In addition, the majority and minority spin bands are fully superposition and therefore the AGaNNRs are non-magnetic. As the nanoribbons width increase, band gaps of AGaNNRs decrease monotonically and become close to their asymptotic limit of a single layer of GaN sheet.

The Structural and Electronic Properties of the Zigzag GaN Nanoribbons: A First-Principles Study

We have performed the first-principles calculations onto the structural and electronic properties of GaN nanoribbons with zigzag edge (ZGaNNRs). The results show that, the lowest unoccupied conduction band (LUCB) and the highest occupied valence band (HOVB) are always separated, representing a semiconductor character for the ZGaNNRs. In addition, the majority and minority spin bands are fully superposition and therefore the ZGaNNRs are non-magnetic. As the nanoribbons width increase, band gaps of ZGaNNRs decrease monotonically and become close to their asymptotic limit of a single layer of GaN sheet. It is found that the fewer coordination number will lead the most electrons to range in higher energy region of the occupancy state.